Recently, there have been made great technological advances in disk recording and playback apparatus (hereinafter referred to as “disk drive”) for recording and playing back data on a disk-shaped recording medium such as a hard disk and an optical disk (hereinafter referred to as “disk”), and its use is expanding not only in application of conventional computers but also in many other fields. There are increasing demands for such disk drives that are capable of higher density recoding, resistant to external disturbance such as shock force so as to prevent a disk and a head slider from damage and maintain stabilized recording and playing back performances, and small in size so as to be mounted on portable equipment. However, it sometimes occurred in conventional disk drives, when subjected to external shock force, that the head slider collided with or came into contact with a disk so as to cause wear or damage to the head slider or the disk, such that data recorded on the disk was destroyed, and even the disk drive itself was damaged.
Therefore, there have been demands for improved shock resistance of head sliders, suspensions, or actuator arms used in disk drives. Since, a head slider, in particular, is held above a disk at a small flying height, it tends to collide with the disk when subjected to shock force. Therefore, it is desired to provide a head slider structure which will, at least, not cause fatal damage to a head slider or disk even when a shock force is applied thereto. However, there are few examples of studies so far made of an optimum form or shape of a surface of the head slider opposite to the disk (hereinafter, referred to as “opposite-to-disk surface”), to improve shock resistance. There have conventionally been made studies to suppress variation in a flying height of a rear end portion of a head slider, where a transducer is provided, against variation in skew angle, atmospheric pressure, and so on.
For example, a structure of a head slider is disclosed in U.S. Pat. No. 6,021,020, which, even when there is variation in skew angle, in atmospheric pressure, in external force due to swinging of the head slider, or in load applied thereto, allows positive pressure and negative pressure applied to the head slider to be maintained in good balance based on such variation. It is stated therein that virtually no change is made, by virtue of the good balance thus obtained, in flying height in the vicinity of the transducer, so that stabilized information recording or playback is made possible. In JP8-227514, there is disclosed a structure in which a distance, to a surface of a disk, from a portion of a head slider at which a transducer is provided is virtually not changed even if an external force to increase a pitch angle is applied to the structure. In U.S. Pat. No. 4,909,223, there is disclosed a method to obtain an optimum form or shape of a surface of a head slider opposite to a disk by calculation with use of molecular gas lubrication equations. Further, in U.S. Patent Application No. 2001/0010612, there is disclosed a structure in which collision of a head slider, due to rolling of the head slider, with a disk is prevented by increasing roll stiffness of the head slider. However, in this structure, spring stiffness, obtained by assuming a viscous fluid film formed between the head slider and the disk to be a spring, is not large enough to cope with shock force.
In all the above disclosures, it is designed to suppress variation in flying height of a rear end portion of a head slider under conditions of varied skew angle of the head slider, varied atmospheric pressure, varied load from a suspension, and so on. However, when these variations are compared with externally applied shock force, the shock force is much stronger. Therefore, it is difficult to say that any of the above disclosures is quite effective against shock force.
At times, when for example a head slider is subjected to a great external shock force, the head slider comes to have a negative pitch angle, i.e., a flying height of a front end portion of the head slider becomes, reversely, lower than a flying height of a rear end portion of the head slider. Under conditions of such a negative pitch angle, a viscous fluid such as air stops entering a space between the head slider and a disk surface. As a result, positive pressure disappears, and thereby the head slider is caused to collide with the disk and become damaged.
Especially, disk drives for use in portable equipment are required to be smaller in disk diameter and, in addition, to be smaller in disk rotating speed. Hence, velocity of viscous fluid flowing through a space between a head slider and a disk becomes smaller than in conventional disk drives. Hence, there arises also a problem with regard to how to realize a slider structure having sufficient shock resistance under conditions of such low fluid velocity.